In supernatant fraction prepared from striatal slices two kinetic forms of phosphodiesterase (PDE) with a low and high apparent Km of cAMP can be measured. Incubation of striatal slices with dopamine (2 times 10 to the minus 7th power M) or apomorphine (10 to the minus 7th power M) causes an increase in the amount of Ca2 ion-dependent regulator (CDR) associated with PDE. The increase in the ratio of CDR versus PDE is also reflected in a change of the kinetic profile of PDE, since only one kinetic form of PDE with a low apparent Km for cAMP is present. Haloperidol (10 to the minus 7th power M) prevents the CDR translocation and PDE activation elicited by dopamine or apomorphine. Transection of the nigra-striatal fibres fails to curtail the activation of PDE by CDR elicited by dopamine receptor stimulation.